5′-xanthylic acid is an intermediate in the nucleic acid biosynthesis process, which is physiologically important in the body of animals and plants, used in food, medical supplies and other various field. Thus, inventors of the invention developed a mutant strain having a resistance to 5-fluorotryptophan, from a known strain Corynebacterium ammoniagenes KCCM 10448 also developed by inventors of the invention, producing 5′-xanthylic acid at a high yield and high concentration rate by a direct fermentation method.
5′-xanthylic acid is an intermediary product of purine nucleotide biosynthesis process and important material for producing 5′-guanylic acid. A widely used method to produce 5′-guanylic acid having fineness and high quality is microorganism fermentation method which produces 5′-xanthylic acid first and converts it into 5′-guanylic acid enzymatically, therefore, to produce 5′-guanylic acid, corresponding amount of 5′-xanthylic acid is necessary. Conventional methods to produce 5′-xanthylic acid are chemosynthesis, deaminization of 5′-guanylic acid which is produced as a result of decomposition of ribonucleic acid in yeast, a fermentation method to add xanthine as precursor material in fermenting medium, a fermentation method to use a mutant strain of microorganism, a method to add antibiotic material (JP 1477/42 and JP 20390/44), a method to add surfactant (JP 3825/42 and JP 3838/42) and so on. Among these, a direct fermentation method of 5′-xanthylic acid by a mutant strain of microorganism is quite advantageous in terms of industrial aspect. Thus, we inventors developed a mutant strain with increased productivity of 5′-xanthylic acid, by modifying the existing character of Corynebacterium ammoniagenes KCCM 10448 into the character of producing 5′-xanthylic acid at a large yield rate.